/Engine/Source/Runtime/Core/Public/Math/UnrealMathUtility.h
Determine the position of an AABB relative to a plane: completely above (in the direction of the normal of the plane), completely below or intersects it
-1 if below, 1 if above, 0 if intersects
static int32 PlaneAABBRelativePosition ( const FPlane & P, const FBox & AABB )